Polybenzoxazole (PBO), polybenzimidazole (PBI) and polybenzothiazole (PBT) and related polymers (hereinafter referred to as PBZ or polybenzazole polymers) are known polymers which can be extruded as fibers or films having a high tensile strength and high tensile modulus which are useful for structural applications. It is known in the art to synthesize PBZ polymers by the reaction of a first monomer having a primary amine group and a hydroxyl, thiol or amine group bonded to an aromatic group in an ortho-position with respect to each other, and a second monomer having an "electron-deficient carbon group." See, e.g., Wolfe et al., Liquid Crystalline Polymer Compositions and Process and Products, U.S. Pat. No. 4,703,103 (Oct. 27, 1987); Tsai et al., Method for Making Heterocyclic Block Copolymer, U.S. Pat. No. 4,578,432 (Mar. 25, 1986); Wolfe et al., Liquid Crystalline Poly(2,6-Benzothiazole) Compositions, Process and Products, U.S. Pat. No. 4,533,724 (Aug. 6, 1985); Wolfe, Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,533,693 (Aug. 6, 1985) and Wolfe et al., Liquid Crystalline Polymer Compositions and Process and Products, U.S. Pat. No. 4,533,692 (Aug. 6, 1985), which are incorporated herein by reference.
In most commonly used monomers, the electron-deficient carbon group is either a carboxylic acid group or a carboxylic acid halide group. For instance, monomers may be 4-hydroxy-5-aminobenzoic acid, terephthalic acid, or terephthaloyl chloride.